Format the shasum files correctly

[twangboy]

What does this PR do?

Fixes issues with the content of the shasum files. They need to work as expected. This means it needs to include the file name. I'm not sure why they weren't created that way to begin with.

Also fixes a few typos and an unneeded if statement.

[PaTHml]

The relative filepath will be included in the output.
Example: (2 spaces between checksum and file)
<some-checksum> linux/svtminion.sh

It's not wrong, but it is something to be aware of as the 'sha256sum --check ' command handling of the filepath will expect it to be present and relative to the working directory.

If there are sample validation commands, it should be clear the folder hierarchy be recreated on download.
If not, the filepath (if present) can be removed to flatten the downloads and validation to the working directory.

Generating:
<some-checksum> svtminion.sh
vs.
<some-checksum> linux/svtminion.sh

If the generated sha256 files are used in automation to validate the release data, then this might be adding inconveniences to that process instead of to the download validation.

Either way is good, just something to keep in mind.

Line comments with '#' can be manually added to the sha256 files if needed.
Example: (excuse the markup escapes)
# My comments
<some-checksum> linux/svtminion.sh

[twangboy]

This is assuming the script and the shasum are downloaded and in the same directory. We're gonna keep it like this. We do the same thing with our bootstrap script.

[twangboy]

Ah, I see what you're saying... we need to remove the full path. You're right. I misunderstood your comments.

[PaTHml]

For the release.yml.
The rest LGTM but I'd need to see a sample output to be sure.